The present invention relates to a lithium secondary battery (hereinafter also to be referred to simply as “battery”) and to a manufacturing method thereof, and more particularly, relates to a lithium secondary battery which is superior in safety and productivity, and to a manufacturing method thereof which is simple and superior in productivity.
In recent years, a lithium secondary battery is widely used as a power source for electronic equipment such as portable communication equipment and a notebook-sized personal computer. In addition, demands for resource saving and energy saving are raised on the background of international protection of the earth environment, the lithium secondary battery is being developed as a motor driving battery for an electric vehicle and hybrid electric vehicle (hereinafter also to be referred to simply as “electric vehicle, etc.”).
This lithium secondary battery is advantageous in that it has high operating voltage and high energy density and can discharge a large current, but is inconvenient in that the rise of a battery temperature caused by abnormalities at the time of charging or discharging, for example, over-discharging due to a short circuit of external terminals, or over-charging due to malfunction of a charging device accompanies the rise of inner pressure resulting in a burst of the battery. Accordingly, the lithium secondary battery comprises a pressure release hole in an electrode cap being its component as a safety mechanism for preventing this burst, and on the inner periphery wall or at the end of the pressure release hole a pressure release valve is disposed. As shown in FIG. 10, conventionally this pressure release hole 18 is disposed in the vicinity of the outer periphery of the electrode cap apart from the central axis of the battery case 24.
However, the pressure release hole disposed in the vicinity of the outer periphery of the electrode cap must be disposed in both of the positive and the negative electrode caps, otherwise, insufficiency in releasing gasses from the center hollow portion of the winding core (which contains a lot of gases to cause inner pressure increase) makes it impossible to prevent the battery from bursting which used to be a problem. In addition, when a pressure release hole is disposed in the vicinity of the outer periphery of the electrode cap, electrolyte solution inlet must be disposed separately, and since the electrode cap requires two holes, the area of the portions to be sealed will become large, giving rise to aptness of leakage of the electrolyte solution, which used to be a problem.
Incidentally, the electrolyte solution inlet is disposed in a position of the electrode cap corresponding to the center axis of the winding core since injection of the electrolyte solution is implemented by inserting the injection nozzle into the center hollow portion of the winding core.
In addition, conventionally, the pressure release valve is configured as shown in FIG. 11 by pressing an airtight ring 44 for fixing with a pressure fixing ring 43 where a hole 42 is provided in a battery case 41 (reference should be made to Japanese Patent Laid-Open No. 11-49217, etc.). However, Japanese Patent Laid-Open No. 11-49217 did not disclose any solving means such as particular shapes of components of the pressure release valve and the fixing pressure at the time of assembly and therefore was not sufficiently satisfactory in pressure release operation performance, although the weight of the battery can be reduced due to a decrease in the number of components.
The present invention was made in view of such conventional problems, and an object thereof is to provide a lithium secondary battery in which improvement in safety and productivity has been planned by disposing a pressure release hole in an electrode cap in a position corresponding to the center axis of the winding core, and improving pressure release operation performance and assembly operation performance of the pressure release valve.
In addition, another object of the present invention is to provide a method of manufacturing a lithium secondary battery which is simple for manufacturing and in which improvement in productivity has been achieved by structuring the electrode cap simply.